1. Field of the Invention
The present invention relates to a disc chucking mechanism which rotates, together with a turn table, a recording medium disc, such an optical disc or a magneto-optical disc, to be disposed on the turn table, to write information into the recording medium disc and read it from the same. More particularly, the invention relates to a disc chucking mechanism for positioning a disc with a magnetic center hub and holding the same.
2. Related Art
In a disc drive which writes information signals into a recording medium disc, such an optical disc or a magneto-optical disc, or reproducing stored information from the same, while rotating the recording medium disc, the disc must be rotated in a state that an optical pickup device faces a recording track on the disc. Therefore, the disc drive is provided with a disc chucking mechanism including a turn table. A rotation/drive mechanism drives and rotates the turn table, together with a disc being put on the turn table at a predetermined location. Examples, of the conventional disc chucking mechanism is U.S. Pat. No. 5,303,098.
In order to reduce the size and thickness of the disc driver, the technique of the publication eliminates the use of a chucking plate, which presses the disc against the turn table from its reverse side by removing a movement of the disc in the directions of the revolution axis of the disc. To this end, the disclosed technique includes a turn table which is driven to rotate and on which a disc with a center hole in to be located thereon, a fitting member to be fit into the center hole of the disc, and a plurality of spherical members being retractably provided in the fitting member while being urged and protruded outwardly of the fitting member by an elastic member, the spherical members supporting the disc on the turn table by pressing the disc against the turn table. When the disc is put on the turn table, those spherical members, which are urged and protruded out of the fitting member, are brought into contact with the upper edge of the center hole of the disc. Accordingly, in this state, the disc in supported on the turn table while being pressed against the turn table, viz., the disc is attached to the turn table.
In the conventional chucking mechanism disclosed in the above publication, the disc never moves in the directions parallel to the axis of revolution of the disc when the disc is chucked, and it is not required to use the chucking plate which presses the disc against the turn table from its reverse side. Therefore, the aim of achieving the size reduction and the thinning of the disc driver is successfully achieved.
In the above-mentioned disc chucking mechanism, to attach the disc to the turn table, the plurality of spherical members are urged and brought into contact with the upper edge of the center hole of the disc, to thereby press a disc against the turn table. The disc is centered at a position where the urging forces of the spherical members are balanced. Therefore, if the balancing-state of those urging forces is lost, the centering position will be shifted from the correct one. Particularly when the spherical members are independently urged, the urging forces of those members are likely to be not uniform. In this case, the centering position will be greatly shifted.
The disc chucking mechanism uses a ring formed with an elastic member made of rubber, for example, for the urging means.
Therefore, the urging forces of the spherical members are relatively uniform. Those members for centering the disc are the spherical members protruded outwardly of the fitting member, and a fixed reference point for positioning them is not present. For this reason, the disc being chucked is movable in the directions parallel to the plane of the disc per se, resulting in a play of the disc. Many factors to decenter the disc exists variations of the composition and the size of the elastic ring, nonuniformity of the forces externally applied when the disc is attached, and others. In this respect, some improvement is required for the disc chucking mechanism.
Additionally, the conventional disc chucking mechanism is complicated in structure, and high in parts working and assembling cost.